Total Synthesis of the Broad-Spectrum Antibiotic Amycolamicin

Establishing the Comprehensive Structure-Activity Relationship of the Natural Antibiotic Kibdelomycin/Amycolamicin

Kibdelomycin (KBD) and amycolamicin (AMM) are potent natural antibiotics effective against antibiotic-resistant Gram-positive pathogens, including vancomycin-intermediate Staphylococcus aureus (S. aureus, VISA), methicillin-resistant S. aureus (MRSA), and quinolone-resistant S. aureus (QRSA). Their antibacterial activity stems from an unprecedented dual mechanism: the lower binding sites occupy the adenosine triphosphate (ATP) binding pocket of bacterial type II topoisomerases, while the upper binding sites disrupt the enzyme dimer interface. This dual action, combined with their unique chemical structures, positions KBD and AMM as promising scaffolds for developing new antibiotics. However, the structure-activity relationship (SAR) of KBD/AMM remains underexplored due to their highly complex chemical structures. In this study, we utilized total synthesis to produce KBD/AMM analogs with various site modifications and evaluated their antimicrobial activities. Our findings establish the first comprehensive SAR for KBD/AMM, paving the way for the development of novel KBD/AMM-based antibiotics.

Identification of Kibdelomycin and Related Biosynthetic Gene Clusters and Characterization of the C-Branching of Amycolose

Many bacterial natural products contain C-branched sugars, including components from the outer cell wall or antibiotically active metabolites. The enzymatic C-branching of keto sugars leading to longer side chains (≥C2) is catalyzed by thiamine diphosphate (ThDP)-dependent enzymes. Chiral tertiary α-hydroxy ketones are formed in this process. The ThDP-dependent enzymes that catalyze C-branching reactions belong to one of three enzymatic superfamilies: decarboxylases, transketolases, and α-ketoacid dehydrogenases 2, but branching of keto sugars has only been demonstrated for decarboxylases. In this study, we showed that an α-ketoacid dehydrogenase is responsible for C-branching of the deoxyketo sugar amycolose in the biosynthesis of kibdelomycin in Kibdelosporangium sp. MA7385. In addition, we characterized an amino transferase in the same biosynthetic gene cluster (BGC) that accepts a sterically demanding tertiary α-hydroxy ketone in a downstream reaction. Subsequently, we identified approximately 400 similar BGCs in silico, suggesting that there is a large diversity of possible ThDP-dependent enzymes catalyzing the C-branching of keto sugars and subsequent modifications.

Approach to the Core Structure of Signermycin B

Among the natural tetramic acids with a decalinoyl part, signermycin B is unique because it contains a cis-decalin. In this paper, we demonstrate that the cis-decalin section of signermycin B can be accessed by an anionic oxy-Cope rearrangement. The substrate, a tricyclic dienol was prepared by an intramolecular Diels-Alder reaction of a masked ortho-benzoquinone, generated by oxidation of an α-methoxyphenol in presence of cis-2-hexenol. After a superfluous bromine on the cycloadduct was removed, reaction of the tricyclic ketone with isopropenylmagnesium bromide led to the tricyclic trienol that underwent the oxy-Cope rearrangement to a cis-decalinone. While we could show, that introduction of the 4-ethyl substituent (signermycin B numbering) is possible by enolate alkylation, the 4-epi-isomer was formed.

Synthesis of C-Alkyl Glycosides from Alkyl Bromides and Glycosyl Carboxylic Acids via Ni/Photoredox Dual Catalysis

C-Alkyl glycosides, an important class of C-glycosides, are widely found in various drugs and natural products. The synthesis of C-alkyl glycosides has attracted considerable attention. Herein, we developed a Ni/photoredox catalyzed decarboxylative C(sp3)-C(sp3) coupling reaction of stable glycosylcarboxylic acids with simple aliphatic bromides to generate C-alkyl glycosides. The method successfully linked several functional molecular fragments (natural products or drugs) to a sugar moiety, showing the extensive application prospects of this transformation. Controlled experiments and DFT calculations demonstrated that the reaction pathway contains a free radical process, and a possible mechanism is proposed.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Total Synthesis of Penicyclone A Using a Double Grignard Reaction

We describe the first total synthesis of penicyclone A, a novel deep-sea fungus-derived polyketide, and a reevaluation of its antimicrobial activity. The synthesis of this unique spirolactone was achieved in 10 steps starting from a known d-ribose derivative. The key steps include a double Grignard reaction for the diastereoselective construction of the chiral tertiary alcohol intermediate, tandem oxidation/cyclization, and photooxygenation, followed by an oxidative rearrangement to introduce the enone functionality.

Total Synthesis of Kibdelomycin

A modular total synthesis of kibdelomycin is disclosed that should enable structure–activity relationship (SAR) studies of this interesting class of antibiotics. The route uses simple building blocks and addresses lingering questions about its structural assignment and relationship to amycolamicin, a recently described natural product reported to have a similar structure. Initial antibacterial assays reveal that both C‐22 epimers (the N‐glycosidic linkage) of the natural product have similar activity while structurally truncated analogs lose activity.